DRILLING FLUID

Abstract: The use in a drilling fluid of an ester obtainable by the reaction of a monobasic carboxylic acid having at most 11 carbon atoms and a monohydric alcohol, wherein the acid is produced by the oxo process.

Description: "Drilling Fluid" This invention relates to drilling fluids, more especially to such fluids for use in well drilling. Drilling of oil or gas wells normally involves the circulation of a fluid through the drill string and out through nozzles in the drill bit, the fluid being returned through the annular passage formed between the drill string and the bore. The fluid cools and lubricates the drill, provides a hydrostatic head to counterbalance pressures, and removes the cuttings from the drill bit. Such fluids are also employed in other areas, for example, goether al drilling, drilling for water and scientific drilling. Oil-containing drilling emulsions have been used for many years for these purposes. The emulsion may be in the form of a water-in-oil or an oil-in-water emulsion, in each case normally having finely divided solids suspended therein, and containing a variety of additives for various purposes, e.g., emulsifiers, surfactants, pH control agents, biocides, corrosion inhibitors, weight and viscosity regulators, oxygen and sulphur scavengers, and fluid-loss additives. It is also possible to have water-free oil drilling fluids. The modern technological and ecological demands on the oil phase components of drilling fluids now make it desirable for the following requirements to be borne in mind. The material should be hydrophobic and of low polarity (to minimize swelling of clays and shales) . It should have as high a flash point as possible, advantageously above 100°C, and preferably above 140°C. Its viscosity at 20°C should be at most 20 cSt (20 mm 2 /s) , advantageously at most 15 cSt, especially at most 12 cSt, and preferably at most 10 cSt, and it should have a pour point below -15°C, to be pu pable between -5°C and -10°C. It should be a poor solvent for CO2 and H2S. It should remain physically and chemically stable at temperatures up to 250°C, pressures up to 8000 p.s.i. (about 55 MPa) and high pH (up to 10 lb of lime per barrel, about 30 kg of lime per m 3 or pH 11) while being biodegradable under aerobic and preferably also under anaerobic conditions. The material and its degradation products should have low toxicity both to mammals and to marine flora and fauna, and little odour. All these desiderata must be borne in mind, as well as the prime purpose of the material, to provide the best possible lubricity. The oil phase was traditionally provided by a hydrocarbon oil, often with an aromatic content; concern for industrial hygiene has recently required that dearo atized hydrocarbon oils be used instead and, more recently, concern for the environment has required that such oils should be biodegradable and should exhibit low toxicity towards aquatic organisms. As hydrocarbon oils frequently do not meet these recent requirements they are increasingly restricted in their use. Many replacements for hydrocarbons have been suggested; these have primarily been aliphatic materials with functional groups that facilitate biodegradation, for example, ester groups. In EP-A-386636, esters derived from monocarboxylic acids having from 6 to 11 carbon atoms and monofunctional and/or polyfunctional alcohols are proposed for use in water-in-oil invert drilling fluids. The monofunctional alcohols preferably have at least 7 carbon atoms. The acids and alcohols may be of natural and/or synthetic origin. In EP-A-374672, esters derived from aliphatically saturated monocarboxylic acids having from 12 to 16 carbon atoms and monofunctional alcohols having from 2 to 12, more especially from 4 to 12, carbon atoms are proposed for use in water-in-oil invert drilling fluids. Although starting materials from natural origins are preferred, the possibility of using synthetic acids and alcohols is also mentioned, in particular, the possibility of making the alcohols by the oxo process is also mentioned. The carboxylic acids are preferably predominantly straight- chain. EP-A-374671 and EP-A-386638 describe various other esters derived from carboxylic acids and alcohols proposed for use in water-in-oil invert drilling fluids. The stability to saponification of the above esters, however, under the conditions in which the drilling fluids are used has up to now proved insufficient, and problems with odour, viscosity increase, and poor separation of cuttings from the fluid have been encountered. There accordingly remains a need for a drilling fluid having improved technical properties which also meets the ecological demands presently being made or likely to be made in the near future. Furthermore there is a need for a biodegradable oil phase for invert drilling muds with lower viscosity and higher flash point, preferably with a low effect on algae growth. In one embodiment the present invention provides the use in a drilling fluid of an ester obtainable by the reaction of a monobasic carboxylic acid having at most 11 carbon atoms and a monohydric alcohol, wherein the acid is produced by the oxo process. Advantageously, the alcohol is also produced by the oxo process. It will be understood by those skilled in the art that the alcohols and acids that are direct products of the oxo process, sometimes hereinafter referred to as oxoalcohols or oxoacids, are normally mixtures. The olefinic feedstock to the oxo process is usually obtained from petroleum, often obtained by oligomerisation of a lower molecular weight product. It is, accordingly, normally a mixture of structural isomers of a given carbon number, and often a mixture of olefins of different carbon numbers, a mixture of Cs and Cg olefinic isomers. The resulting oxoalcohols and oxoacids will, accordingly, also normally be mixtures, either or isomers predominantly of the same carbon number or of entities of more than one carbon number in various proportions. Pure substances, e.g. , 2-ethylhexanol or 2- ethylhexanoic acid are also obtainable, usually indirectly, from the oxo process. The ester is, therefore, generally a mixture of at least two components. The ester components may all have alcohol moieties comprising the same number of carbon atoms, and acid moieties comprising the same number of carbon atoms (which may be the same as or different from that of the number of carbon atoms in the alcohol moieties) , or the ester components may have different numbers of carbon atoms in their alcohol moieties, or in both their moieties. For each ester component, the acid moiety is preferably a mixture of branched isomers, or a mixture of branched and linear isomers, and the alcohols moiety is preferably a mixture of branched isomers, or a mixture of branched and linear isomers. For each isomer, the α-carbon on the acid moiety preferably carries at least one hydrogen atom, and the α- carbon on the alcohol moiety preferably carries at least one hydrogen atom. It has been found that esters of a given chain length having linear moieties have a higher biodegradability but a lower hydrolytic stability and a higher viscosity at the same flash point when compared with branched chain esters. Esters having highly substituted α-carbons on the acid moiety or the alcohol moiety have a higher hydrolytic stability but a lower biodegradability when compared with esters having less highly substituted α-carbon atoms. Such esters are also expensive to manufacture because steric hindrance on the α-carbon reduces the rate of esterification. An ester for use in a drilling fluid must have high biodegradability but must also have high hydrolytic stability and a low viscosity while still being economic to produce. Surprisingly, it has been found that use of esters comprising branched acid moieties or alcohol moieties but having at least one hydrogen on the α-carbon of the acid moiety or the alcohol moiety gives an economically producible product with the optimum balance between hydrolytic stability, viscosity and biodegradability. In addition, the accumulation of toxic species in biological matter is related to the ability of species to migrate through cell membranes. This is dependent on the 3- dimensional size of the species. Accordingly, species having branched moieties will be less efficient than species having only linear moieties at migrating through cell membranes. Whilst not wishing to be limited by theory, the applicants believe that this factor contributes to the improved ecotoxicological properties of esters used according to the present invention. Commercially available oxoalcohols include LIAL alcohols, containing from 30 to 50% linear components, for example LIAL 123, comprising a mixture of C^ to C^ alcohols, SYNPROL alcohols, containing about 50% linear components, for example SYNPROL 35, comprising a mixture of C1 3 to Ci5 alcohols, ACROPOL alcohols, for example ACROPOL 9 or 11 comprising C 9 or C^ alcohols respectively, ACROPOL 91 comprising both C 9 and C^ alcohols, and ACROPOL 35 comprising a C 13 to C 15 alcohol mixture, each with about 65% linear components, NEODOL alcohols, for example, NEODOL 11, 23 and 45, comprising C^ alcohols, a C^ 2 anc c 1 3 alcohol mixture, and a C1 4 and C 3 alcohol mixture respectively, each with about 85% linear components, and EXXAL alcohols, for example, EXXAL 6, 9 and 13, comprising Cg, C 9 or C 13 alcohols respectively, each with less than 1% linear components. (LIAL, SYNPROL, ACROPOL, NEODOL, and EXXAL are trade marks.) Commercially available oxoacids include CEKANOIC acids, for example, CEKANOIC 7, 8, 9, 10, 11, 12, and 13, comprising C7 acids to C1 3 acids respectively, and 2- ethylhexanoic acid. (CEKANOIC is a trade mark.) Advantageously, each alcohol moiety and each acid moiety has at least 6 carbon atoms and preferably at least 8 carbon atoms. By selecting such longer chain alcohols and acids, i.e., those having at 8 carbon atoms, the resultant esters will have an advantageously higher flash point in use as a drilling fluid. The total number of carbon atoms in the ester, however, needs to be minimized if the ester is also to have an acceptably low viscosity. Low ester viscosity aids the separation of cuttings from the drilling fluid, and gives more flexibility in the formulation of the drilling fluid. In general, for an ester of a given molecular weight, it is preferred that the acid moiety contains fewer carbon atoms than the alcohol moiety, such ester having higher flash points that the corresponding esters in which the alcohol moiety contains the lower number of carbon atoms. Although the preferred esters have a slightly higher viscosity, the difference is slight. For example, whereas the C Q oxoalcohol ester of the C 9 oxoacid has a flash point of 143°C, with a viscosity of 6.20 mm 2 /s at 20°C, the corresponding C 9 oxoalcohol ester of the C 8 oxoacid has a flash point substantially higher, at 170°C, with a viscosity only slightly higher, at 6.43 mm /s. Advantageously, each alcohol moiety and each carboxylic acid moiety is aliphatic, and preferably is saturated. This reduces the possibility of unwanted side reactions, for example, polymerisation during production or use of the drilling fluid. The ester used according to the invention advantageously has a flash point above 100°C and preferably above 140°C. The ester, the alcohol, and the acid advantageously all have pour point below -30°C. The low pour point of the ester ensures that it is always pumpable, even in cold conditions, and the low pour points of the alcohol and acid ensure that any free alcohol or acid present in the drilling fluid caused by ester hydrolysis do not crystallise out at low temperatures or on cooler surfaces, for example, on tools which have been in contact with the drilling fluid. Advantageously, the ester has a maximum viscosity of 20 mm 2 /s at 20°C, preferably 10 mm 2 /s at 20°C. The esters proposed for use in the present invention have low surface tensions, compared with the surface tensions of fatty acid esters of the same or similar molecular weight, this being especially true of the oxoalcohol-oxoacid esters. A low surface tension assists in wetting of suspended matter, the build-up of filtercake, and of a lubricating film between the filtercake and drillstring. The ester used in accordance with the present invention is advantageously selected from the group comprising nonyl oxooctanoate, octyl, oxooctanoate and octyl oxononanoate. Advantageously, the octyl and nonyl moieties are also oxo- derived. Decyl, advantageously oxodecyl, oxoheptanoate is also a suitable ester for use in accordance with this invention. The invention also provides the use in a drilling fluid of 2-ethylhexyl 2-ethylhexanoate, at least the acid moiety and preferably the alcohol moiety advantageously being produced by the oxo process, and subsequent oxidation or reduction and, if desired or required, separation, e.g., by distillate, from other moieties produced thereby. The invention also provides a drilling fluid comprising an emulsion, containing an ester as provided by the invention, water, at least one member selected from surfactants and emulsifiers, and at least one member selected from clay, a halide of an alkaline earth or alkaline metal, and weighting material. Advantageously, the emulsion is a water-in-oil emulsion containing less than 50% water, although oil-in-water emulsions are also provided by the invention. The invention further provides a water-free drilling fluid containing an ester as provided by the invention, at least one member selected from surfactants, and at least one member selected from clay, a halide of an alkaline earth or alkaline metal, and weighting material. A water-free drilling fluid reduces the possibility of ester hydrolysis. Advantageously, the drilling fluid also contains lime which, in addition to its normal function as an alkali reserve, protects, inter alia, against corrosion. It is advisable to limit the concentration of lime to a maximum of 0.01 kg per dm 3 of drilling fluid. The esters are made by methods that are per se known, most conveniently by reaction between the acid and the alcohol in the present of a catalyst, or by reaction of the acid chloride with the alcohol. For details of such properties, the reader is referred to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Vol. 4, pp 863 to 871, and Vol. 9, pp 291 to 310; Houben-Weil, Methoden der Organische Chemie, 4 Edition, Band V/3, pp 862 to 873, W.J. Hickinbottom, "Reactions of Organic Compound" (Longmans, Green 1959), pp 291 to 294, and especially "Neoacids - Properties, Chemistry and Applications", Exxon Chemical Americas, 1989, the disclosures of all of which are incorporated herein by reference. As catalyst for direct esterification, there may be mentioned, for example inorganic acids, e.g., sulphuric, hydrochloric, and Lewis acids (usually boron trifluoride) ; organic acids, e.g., p-toluene sulphonic, and methane sulphonic acids, and cation exchange resins, or organometallic catalyst, e.g., tin and titanium compounds. Using the acid chlorides, esters may be formed with, for example, thionyl chloride, phosphorus tri or pentachloride, or phosgene as catalysts. The acids, acid chlorides and alcohols may be used in the pure state or as technical grade products, which contain a range of materials of molecular weights lower and higher than that designated. Example The esters isononyl iso-octanoate was prepared from isononyl alcohol and iso-octanoic acid, both of which are made by the oxo process, the isononyl alcohol by the hydroformylation of octenes and subsequent hydrogenation of octenes and subsequent hydrogenation and the iso-octanoic acid by hydroformylation of heptenes and subsequent oxidation. The ester which was made by standard esterification techniques had the following viscosity properties: Kinematic Viscosity 20°C 6.26 40°C 3.78 100°C 1.42 Specific 5 ^ (60/60°F) 0.8678 Flash Point 157 Cleveland Open Cup Method The ester exhibited ready biodegradability as required for drilling muds and performed well in experimental drilling mud formulations. It also demonstrated low effect on algae growth as tested on skeletonema costatum.

Claims: CLAIMS : 1. The use in a drilling fluid of an ester obtainable by the reaction of a monobasic carboxylic acid having at most 11 carbon atoms and a monohydric alcohol, wherein the acid is produced by the oxo process. 2. The use as claimed in claim 1, wherein the alcohol is produced by the oxo process. 3. The use as claimed in claim 1 or claim 2, wherein the ester is a mixture of at least two components. 4. The use as claimed in claim 3, wherein the ester components have different numbers of carbon atoms in their alcohol moieties, or in their acid moieties, or in both their moieties. 5. The use as claimed in claim 3, wherein all the ester components have alcohol moieties comprising the same number of carbon atoms, and acid moieties comprising the same number of carbon atoms. 6. The use as claimed in claim 4 or claim 5, wherein for each ester component the acid moiety is a mixture of branched isomers, or a mixture of branched and linear isomers. 7. The use as claimed in claim 6, wherein, for each isomer, the α-carbon on the acid moiety carries at least one hydrogen atom. 8. The use as claimed in claim 4 or claim 5, wherein for each ester component the alcohol moiety is a mixture of branched isomers, or a mixture of branched and linear isomers. 9. The use as claimed in claim 8, wherein, for each isomer, the α-carbon on the alcohol moiety carries at least one hydrogen atom. 10. The use as claimed in any of the preceding claims, wherein each alcohol moiety and each acid moiety have at least 6 carbon atoms. 11. The use as claimed in any of the preceding claims, wherein each alcohol moiety and each acid moiety have at least 8 carbon atoms. 12. The use as claimed in any of the preceding claims, wherein each alcohol moiety and each acid moiety are aliphatic. 13. The use as claimed in any of the preceding claims, wherein each alcohol moiety and each acid moiety are saturated. 14. The use as claimed in any of the preceding claims, wherein the ester has a flash point about 100°C. 15. The use as claimed in any of the preceding claims, wherein the ester has a flash point above 140°C. 16. The use as claimed in any of the preceding claims, wherein the ester, the alcohol and the acid have a pour point below -30°C. 17. The use as claimed in any of the preceding claims, wherein the ester has a maximum viscosity of 20 cSt at 20°C. 18. The use as claimed in any of the preceding claims, wherein the ester has a maximum viscosity of 10 cSt at 20°C. 19. The use in a drilling fluid of isononyl isooctanoate, nonyl oxooctanoae, octyl oxooctanoate or octyl oxononanoate. 20. The use in a drilling fluid of 2-ethylhexyl 2- ethylhexanoate. 21. A drilling fluid comprising an emulsion, containing an ester as specified in any one of claims 1 to 20, water, at least one member selected from surfactants and emulsifiers, and at least one member selected from clay, a halide of an alkaline earth or alkaline metal, or weighting material. 22. A drilling fluid as claimed in claim 21, wherein the emulsion is a water-in-oil emulsion containing less than 50% water. 23. A drilling fluid as claimed in claim 21, wherein the emulsion is an oil-in-water emulsion. 24. A water-free drilling fluid, containing an ester as specified in any one of claims 1 to 20, and at least one member selected from clay, a halide of an alkaline earth or alkaline metal, and weighting material. 25. A drilling fluid as claimed in any one of claims 21 to 24 which also contains lime. 26. A drilling fluid comprising an invert emulsion in which the oil phase is isononyl isooctanoate.

Inventors: CAERS RAF, GODWIN ALLEN DAVID, MATHYS GEORGES MARIE KAREL, SOLLIE TOR, CAERS, RAF, GODWIN, ALLEN, DAVID, MATHYS, GEORGES, MARIE, KAREL, SOLLIE, TOR
Applicants: CAERS RAF, EXXON CHEMICAL PATENTS INC, GODWIN ALLEN DAVID, MATHYS GEORGES MARIE KAREL, SOLLIE TOR, CAERS, RAF, EXXON CHEMICAL PATENTS INC., GODWIN, ALLEN, DAVID, MATHYS, GEORGES, MARIE, KAREL, SOLLIE, TOR
Application year: 1994
Main classification: C09K7
IPC codes: C09K8